Synthetic resin, which has not only excellent chemical characteristics but also excellent mechanical characteristics, has been widely used for various fields such as building materials, automobile parts, packing materials, agricultural materials, housing materials for electric appliances and toys. In particular, a polylactic acid resin has a high melting point and can be used for a melt molding, therefore, it is expected as an excellent biodegradable polymer suitable for practical use. In addition it is also expected that it can be used as a polymer for general-use made from bio-raw materials. However, these synthetic resins are flammable substances, therefore, it is essentially required to make them flame-retardant for some applications.
The methods for making these synthetic resins flame-retardant by adding a halogen flame retardant, an inorganic phosphorous flame retardant typified by polyphosphate flame retardants such as red phosphorous and ammonium polyphosphate and an organic phosphorous flame retardant typified by triallyl phosphorous ester compounds, and optionally adding a metallic hydroxide or flame retardant auxiliaries such as an antimony oxide and a melamine compound or the like, alone or in combination are widely known.
However, a halogen flame retardant produces a poisonous gas when burned, which is a problem. Therefore, attempts to use the above phosphorous flame retardant with no such problems have been made. Examples of the attempt such as the flame-retardant synthetic resin compositions which contain an ammonium polyphosphate, a polyhydroxyl-containing compound, a triazine ring-containing compound and a metallic hydroxide (Patent documents 1-5); the flame-retardant synthetic resin compositions which contain melamine polyphosphate and (penta or tripenta) erythritol (Patent documents 6 and 7); the flame-retardant synthetic resin compositions which contain polybutylene terephthalate (PBT), melamine pyrophosphate and aromatic phosphate.oligomer (Patent document 8); and the methods to use melamine pyrophosphate and other phosphorous compounds for polymers such as PBT to make them flame-retardant (Patent documents 9 and 10), have already been known.
Among these methods, intumescent flame retardants have excellent flame retardancy in particular wherein a surface of intumescent layer is formed when burned and flame retardancy is realized by inhibiting diffusion of the decomposition products and heat transmission (Patent document 11).
Further attempts to add an anti-dripping agent to the above intumescent flame retardant have been made in order to inhibit the dripping of resin when burned. It is known that polytetra fluoroethylene (PTFE) is effective as the said anti-dripping agent in particular. However, a fluorinated anti-dripping agent such as PTFE was not a complete non-halogen flame retardant since it has fluorine atoms. Furthermore, using clay mineral or layered mineral as an anti-dripping agent is suggested (Patent documents 12 and 13). However, these did not give any useful knowledge for a flame retardant composition, which is able to form the intumescent layer, wherein not only forming a minute surface of intumescent layer but also inhibiting drip is required.